Highly Proton Conductive Membranes Based on Poly(vinylphosphonic acid)-Coated Cellulose Nanocrystals and Cellulose Nanofibers for Polymer Electrolyte Fuel Cells

Polymer electrolyte membranes (PEMs) are frequently composed of perfluorosulfonic acid polymers (PFSAs) and are used in polymer electrolyte fuel cells (PEFCs). However, PFSAs encounter obstacles such as intense acidity, environmental impact, and high cost. Previous studies have attempted to achieve high proton conductivity in low-acid materials by constructing precise conduction pathways. In addition, nanocellulose is a promising new membrane material for PEFCs with a much lower environmental impact and cost than PFSA. In this study, nanocellulose-based membranes were produced by using polymer-coated cellulose nanocrystals (CNC), and cellulose nanofibers (CNF) as a binder. The nanocellulose-based membranes demonstrated a maximum conductivity of 9.2 x 10(-2) S/cm, which was comparable to that of PFSAs, even though approximately 80% of the components were nanocellulose. This could be attributed to the creation of highly proton-conducting pathways at the interface between the hydrophilic layers of CNC-polymer, and the water uptake and retention properties of CNF. This result suggests that nanocellulose presents a high potential substitute for PFSAs and serves as a pivotal component in the forthcoming age of environmentally sustainable PEMs. In addition, nanocellulose exhibits exceptional features that make it suitable for use as a binder in secondary batteries.